1. Field of the Invention
The invention relates to data communications in general and more particularly to circuit arrangements or adapters for attaching computers to a communications highway.
2. Prior Art
Digital data communication between personal computers and a remote host computer installation is coming into widespread use. A typical communications network that facilitates digital data transmission usually consists of a protocol conversion circuitry, an EIA interface circuitry, and a modem. The protocol conversion circuitry transforms the digital data into one of the well-known control protocols, namely SDLC (Synchronous Data Link Control), Asynchronous (Async), High Level Data Link Control (HLDLC), (Bisync), Advanced Data Communications Control Procedure (ADCCP), etc. The EIA interface circuitry conditions signals outputted from the protocol converter and supplies said signals to the modem from whence the signals are transmitted through telephone lines and/or equivalent narrow band communications channels.
The prior art has provided both single and multiple type protocol converters. The single type protocol converter can only transform data into one type of protocol whereas the multi-protocol converter can transform data into one of a plurality of protocols. Examples of the prior art protocol converters are set forth in U.S. Pat. Nos. 4,494,186; 4,467,445; 4,513,373; 4,504,901; 4,519,028; 4,500,933; 4,494,186. Arguably, these protocol converters work well for the intended purpose. However, a general drawback is that the circuitry of the adapters is very complicated and cannot be easily used with pre-existing microcomputers. Any attempt to use the prior art protocol converters with pre-existing computers (be it personal or otherwise) requires extensive changes in the computer's architecture and/or the computer's programming.
Because of the stated impact, it would seem as if there is a need for a multi-protocol converter that is compatible with the architecture and/or programming of pre-existing computers. Such a multi-protocol adapter can be easily mounted in the computer and provides the facility whereby the computer may communicate with a remote host, etc.